Effusivity is a measurement that combines thermal conductivity, density, and heat capacity.
The effusivity of a material (sometimes called thermal inertia) is the square root of the product of the thermal conductivity, density and heat capacity. The effusivity of your hand and the object it touches determines the interfacial surface temperatures of your hands. If the effusivity of a material is high-as with ceramic, the interfacial temperature is lower than if the effusivity is lower-as with wood. This is why a wood floor feels warmer than a ceramic floor, and why a carpeted floor feels warmer still.
As a natural characteristic of materials, each has a different effusivity from the other. Effusivity is sensitive to composition in view of the fact that materials differ in value from 5 Ws1/2/m2K for air to several thousand for advanced composites.
In order to measure effusivity, a suitable probe such as that provided for U.S. Pat. No. 5,795,064, issued Aug. 18, 1998, to Mathis, may be used, the entire disclosure of which is hereby incorporated by reference.
In the pharmaceutical industry, when powdered components are blended during drug production, time is a critical factor. Typically, when a drug formulation is developed, bench-scale amounts are synthesized and subsequently scaled up through a series of steps to 1000 kg blending equipment. One of the key limitations in the field is that optimum mixing time of the components has to be established by trial and error. Blending for an insufficient amount of time fails to mix the samples, while over blending causes segregation. It is also a significant problem that over blending is time consuming and the added frictional heat can thermally damage the sensitive components in the mixture.